James Ellroy writes mostly very long novels, in a crime-horror crossover genre, set in the Fifties America of his childhood.

American Tabloid is something of an exception in that, although it runs to a characteristic 600 pages of skulduggery and splat, the action extends from 1958 all the way up to 1963, encompassing the assassination of President Kennedy, or almost: it actually stops a few minutes before the shooting, as if to say that the rest is history, or perhaps to differentiate this work from Don de Lillo's novel Libra, which dealt with similar material.

It is not too clear whether the title refers to the scandal-sheet on which a small part of the multifoliate plot depends, or to the style in which the whole novel is written. There are very few paragraphs longer than three lines, and Ellroy uses block capitals instead of italics for emphasis. This remains a vivid and effective approach for a long stretch but does become monotonous and wearing.

The three anti-heroes are Big Pete Bondurant, a French-Canadian hitman working for the Teamsters' union chief Jimmy Hoffa, and two renegade FBI men, Kemper Boyd and Ward Littell. Boyd is a Southern smoothie assigned by the evil J. Edgar Hoover to infiltrate the Kennedy circle and spy on Bobby's crusade against organised crime (Hoover maintains that there is no Mob and doesn't want the Bureau made to look stupid); Littell is a conscientious wimp on a self-appointed mission to uncover the accounts of the Teamsters' secret loan fund.

Boyd, sent by Bobby to investigate Mob dealings in Miami, finds he can make more money by stringing for the CIA as a licensed drugs and arms dealer, gearing up the anti-Castro Cuban exiles for the Bay of Pigs invasion and also taking commissions from the Mob, who want their Havana casinos back.

Littell, thrown out of the Bureau for drinking and disobedience, is offended by Bobby's refusal to give him a job in the new Kennedy administration and becomes a Mob lawyer instead. He and Boyd have meanwhile recruited Big Pete, whom they once arrested for something minor, as an all-purpose gofer and killer.

After the Bay of Pigs fiasco, seeing JFK as soft on Cuba, Littell and Pete seek to compromise the President by setting him up with a gorgeous redhead singer, Barb Jahelka, and bugging the hotel room. Boyd finds out, pulls the plug, but gets the blame and the sack from Bobby all the same. The three men then put together a Mob- sponsored plan to kill JFK during a motorcade in Miami.

The story tends to disappear up its own fundament. The Mob scrub the operation because there's a better plot in the works to do the job in Dallas a week later. (Oddly, Ellroy claims the Miami motorcade was cancelled in any case. It wasn't, and went ahead without a hitch.) Pete marries Barb, though God knows what she sees in the creep. Littell shoots Boyd for no apparent reason whatever.

There are many more convolutions along the way, most of them fairly nasty. Ellroy has rather a pronounced relish for mayhem and violence. When Boyd and Pete steal one of Castro's dollar-earning heroin shipments by shooting the landing party on the beach, they chainsaw the bodies up before throwing them into a tide pool full of sharks. It is a long, grisly and indeed gristly process, which the reader gradually realises is completely gratuitous. If you've got sharks, you don't need chainsaws.

In close-quarter gun battles, Ellroy's guys are always getting sprayed with the victims' blood and having to wipe it out of their eyes before they go on firing. The writer may be confusing Hollywood shock-effects with life. If you're the shooter, you're facing the entry wound, which is all but bloodless. Any blood will fly from the exit wound and away from you. And in common with most splat-artists Ellroy luridly overrates the blast power of small arms. Even a whole clip of .45 slugs is unlikely to take someone's head off.

Perhaps he is influenced by the thought of poor JFK's terrible head wound, which most of us have seen on film. But that was a 7.62mm high-velocity rifle round at work, not a mere pistol slug; and besides, a Guards officer on Tumbledown sustained a near-identical injury, losing 40 per cent of his brain tissue, and is still with us. Guns do not necessarily grant omnipotence.

Again, for some reason Ellroy keeps having his characters use silenced revolvers. Automatics you can silence, because the breech is airtight at the moment of firing, but a revolver's cylinder is by no means an airtight fit, so the bang gets heard even if you muffle the muzzle.

Another technical goof afflicts the characters themselves. All three of our main men go through personality changes and reversals which are psychologically not on. We seem to be presented, from time to time, with a different set of people under the same names. The worst case is Littell, but it is also curious how Ellroy comes to portray Pete as a lovable foursquare hunk even while crediting him with the absurd total of 300 men killed.

Ellroy transparently hates JFK as a "charming, shallow man" of inadequate sexual performance - "Two-Minute Jack", "Bad-Back Jack" - but in this fictional world the President still comes across as the finest and nicest man there is, apart from Bobby. Whenever the Kennedy brothers appear and speak, the book springs to life as it does at no other time, though the slimy Hoover is drawn with some wit, and the luscious Barb is a nice touch. Her tough-minded intelligence is well evoked, and her physical presence too - Pete notices she smells of suntan oil and thinks, "Redheads and stage lights. . ."

Ellroy might do better to give us more of this understated, dry, humane treatment. That way we might need less of the hyper-hyper, slam-bang, perverse wish-fulfilment stuff.